Magnetic tape drives are typically employed to provide data backup and archival storage for user data records and programs. For digital data storage applications, tape drives typically employ either rotating heads, or non-rotating heads. One form of non-rotating head is the streaming tape drive. In a streaming tape drive, multiple blocks of user data are typically written to tape in a single streaming operation, rather than in a series of start-stop operations of the tape transport. In the streaming tape drive, a magnetic tape head includes at least one write/read element. The head is typically positioned laterally relative to the tape path by a lead screw, which is controllably rotated by, e.g., a stepper motor, or an equivalent arrangement. In this manner, a single transducer element, or several spaced-apart elements, may write to, and read from, a multiplicity of linear tracks defined along the magnetic recording tape.
In order to permit the head to be moved laterally across the tape in order to confront the multiple parallel tape tracks, a flexible head interconnector arrangement is needed to connect the write/read elements of the head to electronic circuitry conventionally mounted on one or more printed circuit boards affixed to the tape drive base or housing. In the past, flexible wires, twisted together into pairs and gathered into a cable, have been employed as tape head interconnects.
Data rates and track densities are increasing. One way to increase the data rate of a magnetic recording system is to increase the write frequency. Another way to increase data rate is to increase the number of parallel write and read elements of the head and data channels of the tape drive so that more tracks are simultaneously written during each tape streaming operation.
A further way to increase track density is to reduce the linear track width and spacing by aligning the write elements/read elements closer together. By employing thin film inductive write elements and magneto-resistive read elements, it is practical to increase the number of data tracks. Since the head carrying the write and read elements must still be displaced laterally relative to the tape path, a flexible interconnect arrangement is needed in order to connect the write and read elements of the movable head to the write and read electronics affixed to the printed circuit board of the drive electronics.
Write system bandwidth is one of the constraints in achieving higher data rates in high-performance tape drives. One approach to improve the write system bandwidth and rise time is to reduce the parasitic inductance and impedance of the write system by using a two-layer flexible circuit design, with write trace pairs stacked on top of each other, using both trace layers of a dual layer flexible circuit. This configuration results in higher capacitance, but much lower inductance compared with the more traditional layout with write trace pairs on the same trace layer. The lower inductance allows for much faster write current rise time response, which enables the higher system bandwidth and transfer rates needed for higher performance tape drive systems.
FIGS. 3A and 3B depict a dual layer flexible circuit employing paired traces on the layers to illustrate a concern with such arrangements. FIG. 3A shows a plurality of write trace pairs formed on a dual layer flexible circuit. Each write trace pair includes a first write trace 50 and an opposing second write trace 52 formed on opposite sides of a substrate 51. The first and second write traces 50, 52 of a write trace pair are of similar dimensions and formed of copper electrodeposited upon the substrate 51, for example. The structure of FIG. 3A depicts an ideal alignment of the first and second write traces 50, 52 in the two layers. In practice, however, the use of paired traces on two layers of a flexible printed circuit can be inhibited by variation in the layer-to-layer alignment of the traces. See, for example, FIG. 3B which depicts an exemplary dual layer flexible circuit with a misalignment of the trace layers. As can be seen, variation in the alignment of the two traces between the layers changes the effective separation between the write traces. This variation in the alignment of the two traces between the layers will produce variations in the capacitances and inductance of the full circuit, which is an undesirable result. In high performance multi-channel tape drives, there will also be multiple pairs of write traces, and layer to layer alignment variation also presents a challenge in maintaining low crosstalk between adjacent pairs of write trace pairs.
One approach to compensate for this alignment issue is to use very wide circuit traces, along with very wide spaces between the traces of adjacent circuits, so that the effect of the layer-to-layer misalignment on capacitance, inductance and crosstalk is minimized. However, this approach results in a much larger overall width for the flexible circuit, presenting cost and mechanical integration challenges.